Integrated circuit components continue to shrink in size, and demands in battery-powered devices continue to increase. Reference current circuits are widely used in integrated circuits to generate bias currents. However, as supply voltages fall, some commonly used reference current circuits can no longer operate or operate poorly under low voltage conditions. Thus, the supply voltage represents one of the challenges in the design of reference current circuits. Most analog systems are supplied with a battery voltage. Generating a reference current from a battery voltage generally provides good performance in terms of leakage current and output resistance, but with a relatively high power consumption. Generating a reference current from a low supply voltage enables a small silicon area and low power consumption, but requires the use of core devices that have the drawbacks of current leakage and low output resistance. Further, as the supply voltage decreases, conventional reference current circuits may not function properly. Another challenge is the low noise requirement. A low noise reference current circuit requires filter capacitors, however, a gate leakage current flowing through the filter capacitors causes a voltage shift in the current mirror circuit of the reference current circuit, thereby affecting the matching of the current mirror circuit. Yet another challenge is the required accuracy of the reference current circuit. Thus, a low supply voltage faces the problems of a current leakage that can significantly affect a current mirror performance, and a low output resistance of a current mirror may require an output buffer to drive an output load.
Accordingly, there is a need for improved circuits for generating an accurate low-noise current reference with low supply voltages.